The present invention relates to the alignment of camera systems, camera systems as well as an alignment aid for the alignment of camera systems.
Initially, a problem occurring frequently in camera systems will be illustrated based on FIG. 1. FIG. 1 shows a panoramic camera system with cameras 900, whose entrance pupils 902—here, for simplicity reasons, each illustrated as being in front of the objective of the camera 900—are arranged on a common circle 904, such that the cameras 900 are directed radially outward in different directions. FIG. 1 shows, in a shaded manner, critical zones where parallax errors occur, caused by too great a distance of the entrance pupils 902 of adjacent cameras 900, independent of whether a star-shaped or mirror-based structure is selected for the arrangement of entrance pupils.
Usually, a mirror system is used. Thereby, it is possible to place the virtual entrance pupils of all cameras, i.e., virtual images of the real entrance pupils, behind the mirror segments in a common virtual camera center. With such positioning, illustrated in FIG. 2A, where C indicates the common position of the virtual entrance pupils, parallax-free pictures are possible. However, the mirror system has the effect that the captured subimages of the cameras have no overlap, which makes perfect joining, i.e., stitching of the subimages impossible in practice. In earlier applications, such as in theme parks, this had been circumvented by a segmented inaccessible screen, which avoided the necessity of seamless image generation. Recent systems, however, use a tradeoff in the technology, where all cameras are placed such that the virtual entrance pupils lie on a small circle around the intended optimum center. This is illustrated in FIG. 2B, where the circle around the common center C is indicated by 906, the virtual entrance pupils are provided with reference number 908 and the intersection of the mirror segments with the plane in which the virtual entrance pupils 908 lie is indicated by 910. Thus, the arrangement of FIG. 2B does not suffer from the problems in the radial directions 912, where the mirror segments border on one another, since the subimages of the cameras get the necessitated overlap, without the resulting parallax error causing significant limitations. FIG. 3 shows a stereoscopic image of the panoramic camera system with the arrangement of the virtual entrance pupils according to FIG. 3B, wherein the mirror arrangement 912 and the associated cameras 914 can be seen.
The accuracy of positioning the cameras and their entrance pupils determines the extent of the parallax and, hence, essentially the precision of the seamless panorama generation, i.e., stitching. In the scene to be captured, parallax errors can only be accepted subject to specific restrictions. If, for example, only objects in the far range lie within the stitching regions, a greater parallax error will be acceptable than for objects in the near range. The respective criterion is that the resulting parallax error is smaller than one pixel. In order to keep the parallax error sufficiently small to comply with this criterion, very exact positioning of the virtual entrance pupil 908 is necessitated. This again necessitates exact positioning of the cameras and, hence, exact and time consuming calibration, which is accompanied by two essential disadvantages:                The very high effort for exact mechanic positioning of the cameras.        For all degrees of freedom, the cameras need to be able to be moved precisely and to be locked permanently.        The position of the centers of rotation for rotational degrees of freedom cannot be arbitrarily selected. Centers of rotations ideally coincide with the entrance pupils.        Changing a degree of freedom should not result in any further change of other degrees of freedom, i.e., the degrees of freedom are to be orthogonal to one another.        The degrees of freedom are not to change over time, in particular also not by shock or thermal influences.        Determination and control of the desired position.        The exact position of each individual camera resulting from the desired virtual center cannot be readily measured directly. Usually, the same lies within the optics.        When adjusting the optics, the position of the entrance pupils might change.        Additionally, the exact position depends on the residual optical system, such as tolerances of the mirrors.        Determination and control of the common center is performed indirectly via visual control based on the camera images with the help of expensive measurement technology.        Already very small deviations and angle errors have severe consequences and very quickly result in unacceptable parallax errors.        
The above requirements result in a very high equipment effort both for the camera system and for the alignment aids, and the calibration is very time-consuming. Even with optimum equipment prerequisites, alignment and control are only possible with expert knowledge and are very time-consuming, which opposes, in practice, the high cost pressure of commercial productions, in particular for live broadcast.
In the system of FIG. 3, for example, all cameras 914 are mounted individually on a holder 916, in order to be individually orientable and lockable in their positions. In this way, for example, each camera 914 is individually translatable in three spatial directions, rotatable around the optical axis and tiltable around two transversal axes. The resulting sixth axis adjustments are to be performed individually for all cameras 914. Obtaining the configuration of, for example, FIG. 2B in this manner is very expensive.